Bacteria in the genus Staphylococcus are pathogenic to man and other mammals and are traditionally divided into two groups on the basis of their ability to clot blood plasma (the coagulase reaction). The coagulase-positive Staphylococci constitute the most pathogenic species S aureus and whilst coagulase is a marker for S aureus there is no direct evidence that it is a virulence factor. There are over 30 species of coagulase-negative staphylococcus (CNS) and these are common commensals of skin, although some species can cause infections. S. saprophyticus, is a CNS species that is part of the normal vaginal flora and is predominantly implicated in genitourinary tract infections in sexually-active young women. In recent years, several other Staphylococcus species have been implicated in human infections, notably S. lugdunensis, S. schleiferi, and S. caprae. However, the most prevalent CNS species is S. epidermidis which is a commensal of the skin and can also be found in mucous membranes. Little is known about how S. epidermidis causes disease in humans but colonisation of medical devices has led to an acknowledgement of the significance of CNS in infection. A characteristic of many strains of this microbe is the production of a capsule or slime resulting in the formation of a biofilm. In a biofilm, S. epidermidis is protected against attacks from the immune system and against antibiotic treatment, making S. epidermidis infections difficult to stop. Although S. epidermidis is usually non-pathogenic, these bacteria are responsible for a growing number of infections among hospital patients whose immune systems are weakened or compromised and in immuno-competent individuals with indwelling medical devices. Such infections often occur because the bacterium is carried from the surface of the skin to deeper tissues and the blood stream by insertion of venous catheters or peritoneal dialysis catheters. These infections can be both nosocomial or community acquired, but they are more of a threat to hospital patients. This is in part due to hospitals harboring more virulent strains of the organism and the continuous use of antibiotics and disinfectants. S. epidermidis is a major concern for individuals with catheters or other surgical implants because it is known to cause biofilms that grow on such devices, especially on intravenous catheters and on medical prostheses. Infection can also occur in dialysis patients or anyone with an implanted medical device that may have been contaminated. S. epidermidis has also been associated with endocarditis and occurs most frequently in patients with defective heart valves. It is also responsible for many cases of late-onset sepsis in newborns.
As S. epidermidis is part of the human normal flora, it has developed resistance to many common antibiotics such as methicillin, novobiocin, clindamycin, and benzyl penicillin. Most infections require treatment with antibiotics that are effective, such as vancomycin (although cases of S. epidermidis resistant to vancomycin are now appearing), rifampin, linezolid, quinupristin/dalfopristinand and newer quinolones such as gatifloxacin and moxifloxacin. In addition, effective treatment usually requires removal of any implanted medical device that is infected with S. epidermidis, such as indwelling venous catheters, and prosthetic (artificial) heart valves and joints. The pathogenicity of CNS species is related to their ability to form biofilms especially on plastic medical devices and is a major virulence factor.
To survive during colonization or infection of the human body, microorganisms must circumvent mechanisms of innate host defense. Antimicrobial peptides (also known as natural antibiotics) represent a key component of innate host defense, especially in phagocytes and on epithelial surfaces. Antimicrobial peptides derived from humans and other higher animals are potent, broad-spectrum antibiotics and those of bacterial origin tend to have a more focused spectrum of activity. Both types of peptide demonstrate potential as alternative novel therapeutic agents. The interaction of the peptides with susceptible cells is thought to occur via ionic interactions and results in cell death by destabilization of the membranes and/or pore formation. Although there have been several reports in the literature regarding the use of antimicrobial peptides to treat S. epidermidis infections no suitable therapeutic has emerged.
The increasing resistance of CNS species to many synthetic antibiotics emphasizes the urgent need for new and more effective antimicrobial agents. There is a need for new and effective preventive and therapeutic treatments for CNS species infections.